1. Field of the Invention
The present invention relates generally to a transmitting/receiving apparatus and method for an Interleaver Division Multiple Access (IDMA) system. In particular, the present invention relates to an apparatus and method for determining at a receiver the number of transmission layers, a modulation order, and a coding rate adaptively according to the channel states and transmitting signals according to the determined feedback information from the receiver.
2. Description of the Related Art
There have been proposed various schemes for allowing many user terminals to gain multiple access to a central device (for example, a base station). Typical examples of the multiple access schemes are Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), and Space Division Multiple Access (SDMA) schemes. An Interleaver Division Multiple Access (IDMA) scheme, which allows users to gain multiple access by using different interleaving schemes, is emerging as a new multiple access scheme.
The upcoming communication systems are expected to use some of the above multiple access schemes in combination. An example of the combination-type multiple access scheme is to apply the SDMA scheme and/or the IDMA scheme to an Orthogonal Frequency Division Multiple Access (OFDMA) scheme that is regarded as a promising candidate for the next-generation communication scheme.
A Direct Sequence-Code Division Multiple Access (DS-CDMA) scheme extends the bandwidth of a user by a spread sequence. Unlike the DS-CDMA scheme, the IDMA scheme extends the bandwidth of a user by a channel code having the high error correction capability of a low coding rate and discriminates between users by different interleavers. A receiver detects each user signal using a multi-user detection scheme linked with a channel decoder.
The IDMA scheme can be used in combination with a Multiple Input Multiple Output (MIMO) scheme. The IDMA scheme may be adopted in the next-generation communication system. In this case, the number of transmission layers, a modulation order, and a coding rate must be changed adaptively according to the channel states, for maximization of the transmission efficiency (for example, throughput). However, no method has been proposed to determine the number of transmission layers, a modulation order, and a coding rate adaptively according to the channel states in the conventional IDMA system.
Accordingly, there is a need for an improved apparatus and method capable of determining the number of transmission layers, a modulation order, and a coding rate adaptively according to the channel states in the conventional IDMA system.